Analysis of Coal Fractions Using Dibromotriphenyl-Phosphorane: A Selective Ether Cleaving Reagent

Dibromotriphenylphosphorane (DTP), in acetonitrile at 40°C, was found to cleave benzyl phenyl ether in preference to di-alkyl or other aryl alkyl ethers. Competition between 10 mmoles benzyl phenyl ether and 10 mmoles di-n-octyl ether for 0.92 mmole of DTP gave 48% cleavage of benzyl phenyl ether and 1.3% cleavage of di-n-octyl ether based on DTP. Reaction of benzyl phenyl ether and di-n-octyl ether separately with DTP at 40°C produced 80% and 8% cleavage, respectively. Reactions of DTP with diphenyl ether, butyl phenyl ether, phenyl cyclohexyl ether and benzyl benzoate at 40°C produced less than 3% cleavage in all cases. Reaction of the toluene-insoluble, pyridine-soluble fraction of Illinois No. 5 coal (MWn = 1040) with DTP produced fractions containing phosphorus and bromine with lower number average molecular weights. Treatment of the DTP-reacted fractions with 10% HCl/CH3CN produced one fraction of which the MWn of the pyridine-soluble portion was 3150, and another fraction the MWn of which was 2239, with 67.3% of the original carbon recovered (from the total DTP-reacted fraction) and 63.6% of the original carbon recovered (based on the original coal fraction), respectively. The solubility of the DTP-reacted fractions in pyridine decreased. From IR spectra, elemental and molecular weight analyses and the reactions of model compounds, it is proposed that DTP is cleaving benzyl ether linkages in the pyridine-soluble, toluene-insoluble fraction of Illinois No. 5 coal to form reactive fragments which upon further manipulation react to form higher molecular weight aggregates